Abrupt exciton quenching in blue fluorescent organic light-emitting diodes around turn-on voltage region

Abstract

The quenching of electrically generated excitons in organic light-emitting diodes (OLEDs) serves as a limiting factor in fully exploiting the potential of organic emissive materials, ultimately resulting in a reduction of electroluminescence (EL) efficiency. As the quenching yield is contingent upon the density of species such as excitons and polarons, extensive efforts have been made to comprehend the mechanism under high excitation conditions. Herein, we present a sudden exciton quenching at the turn-on voltage region in a blue triplet–triplet upconversion (TTU)-based blue fluorescent OLED that limits overall EL efficiency. We confirmed that the photoluminescence intensity was quenched by ∼5% before injecting a current density of 0.1 mA cm−2. The quenching behavior strongly depended on the hole-transporting materials (HTMs), indicating that a specific radical cation of the HTMs triggers exciton-polaron annihilation events at the interface between the hole-transporting layer (HTL) and the emitting layer (EML). Furthermore, the voltage dependence of exciton quenching yield and EL spectra suggests a shift in the emission zone from the interface to the bulk of the EML with increasing voltage. These findings are critical for designing an optimized HTL/EML interface for highly efficient blue TTU-OLEDs.